Fluoroelastomers are well known in the art. Many are copolymers of vinylidene fluoride (VF2) with at least one other fluorinated comonomer such as hexafluoropropylene (HFP), tetrafluoroethylene (TFE), or a perfluoro(alkyl vinyl ether). Other fluoroelastomers include copolymers of tetrafluoroethylene with a hydrocarbon olefin such as ethylene or propylene and copolymers of tetrafluoroethylene with a perfluoro(alkyl vinyl ether).
Fluoroelastomeric compositions can be molded into articles having excellent resistance to aggressive chemicals and high temperatures. They have the disadvantage, however, that compared with other heat resistant elastomers such as silicones, fluoroelastomeric compositions demonstrate relatively poor processability in terms of ease of mixing, ease of molding/demolding and flow during injection molding processes.
To provide better processability, processing aids are usually added to fluoroelastomeric compositions. Commonly used processing aids migrate to the surface during processing and it is generally believed that the processing advantage is provided at the interface between the fluoroelastomeric composition and the metal surfaces of the process equipment, e.g., the mill rolls, extruder screw and barrel, or mold cavities and runners. While these processing aids provide processing advantages in the short term, they eventually result in a deposit at the mold surface which is usually termed mould fouling and eventually causes processing difficulties. The surface deposit promotes adhesion between molded components and the mold surface and impairs demolding. It also results in surface defects on molded components such as knit lines. The only remedy is to clean the mold surface at regular intervals which results in a loss of productivity. These processing aids can also interfere with bonding performance, in the case of components having metal bonded inserts, and interfere with the physical properties of molded components, e.g. resulting in increased compression set resistance and lower heat resistance.
Examples of such processing aids include hydrocarbon waxes, natural vegetable waxes, fatty acid esters, mono-functional hydrocarbon amines (e.g., octadecyl amine), organosilicones, and long chain alcohols.
It is an object of the present invention to provide a curable fluoroelastomer composition having various advantages to prior art compositions, including:—improved compound mixing due to improved mill release (in the case of mill mixing) or rotor release (in the case of internal mixing);—improved processing during molding (injection or compression) defined by an easier flow in the mold, a better mold release (less tendency to stick in the mold), a lower level of mold fouling and hence a reduced frequency of mold cleaning; and—improvement in the physical properties of cured and postcured compositions, e.g. lower compression set.